Subsequent to my post about will power and rules, my sister sent me an article about decision fatigue and will power fatigue. Apparently, decision-making and self-control take up energy, and if you have to make many decisions or exert continued will power, you end up in a state of ego depletion, a condition of low mental energy that can lead to poor self-control and bad decisions. In ego depletion, your brain is too tired to weigh advantages and disadvantages, and resorts instead to one of two strategies: you become reckless and obey impulses rather than thinking decisions through (e.g., yes, I should buy these shoes, eat this entire pie, take this shortcut through a deserted park at night), or you avoid making decisions by sticking to the status quo (e.g., I'll just get the same bottle of wine I always get; I'll just continue dating this person for now).
Decision fatigue occurs a) when you have to make decision after decision, and b) when your blood sugar is low. One of the studies cited in the article found that Israeli prison parole boards more often granted parole to prisoners whose cases were reviewed first thing in the morning or right after lunch. In contrast, prisoners whose cases were reviewed right before lunch or at the end of the day were less likely to be granted parole; suffering from low blood sugar and decision fatigue, the parole board couldn't undertake the mental work of evaluating cases and therefore opted to stick to the status quo (i.e., prisoners remain in prison).
Decision fatigue can happen in any situation that requires numerous or repeated decisions. Imagine sitting down with a decorator to outfit your new home. At the beginning, you and your partner eagerly contrast and debate the merits of various dimmer switches, cabinet knobs, and shades of hardwood; after a long day during which you choose from thousands of options for lighting, counter-tops, and flooring, when the decorator pulls out paint chips, you're liable to groan and say "Just paint the whole thing cream!" To avoid hasty or bad choices in decision-heavy situations (e.g., wedding planning), your best bet is to make your choices when you are well-fed, and in more than one session.
Will power fatigue occurs when you have to exert repeated or prolonged self-control. Will power fatigue explains why, when you're trying to cut back on drinking, you're able to turn down champagne at a wedding the first few times it's offered, but by midnight, you're so depleted from saying no that you grab and chug three glasses. Will power fatigue also explains why, after months of resisting your gorgeous, flirtatious, available co-worker, one night you give in and cheat on your partner. To avoid will power fatigue, your best bet is to get out of the situation that requires continued will power (e.g., tell the waiters at the wedding that you don't drink, so they won't keep offering to fill your glass; don't go to post-work cocktail hour when your co-worker is there).
Are some people more prone than others to ego depletion from will power or decision fatigue? According to one of the researchers interviewed for the article, self-control and good decision-making aren't personality traits; rather, the people with these skills are the ones who organize their lives to conserve will power and avoid decision fatigue. They don't go to all-you-can-eat buffets, browse online for items they can't afford, or schedule important meetings late in the afternoon. Further, they establish routines or habits that prevent them from having to make decisions or exercise will power.
Here's where my post about rules fits in. If you have a strict routine of going to the gym after work Monday through Thursday, or a rule that you never watch TV on weekends, you don't have to use will power or make decisions; it goes without saying that you're going to work out four times per week and you aren't going to stream the latest episode of House until Monday. If your firm rule is that you only eat dessert on special occasions, you don't have to decide and redecide every time you walk by the plate of cookies some demon left in the lunchroom at work.
In this way, rules, routines, and smart planning allow you to conserve will power and save your decision-making energy for important decisions or unexpected situations.